The discussion below is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
Small computing devices such as mobile phones and personal digital assistants (PDA's) are used with an ever increasing frequency. The computing power of these devices has allowed them to be used to access and browse the internet as well as store contact information, review and edit text documents, and perform other tasks. Additionally, it has become very popular to send and receive text messages with mobile devices. For example, The Short Message Service (SMS) for mobile phones has been a tremendous success in the text messaging roadmap. As a result, these devices provide many applications in which text entry is required. Unfortunately, such text entry on mobile devices can be cumbersome because they lack a standard full-sized keyboard.
Currently, there are two common ways to achieve text input using numeric key pads found on most mobile phones, a multiple-tap approach, and a single-tap approach. With the multiple-tap approach, a user presses a numeric key a number of times to enter the desired letter, where most of the numeric keys are mapped to three or four letters of the alphabet. For example, the 2 key is usually mapped to the letters A, B, and C. If the user presses the two key once, the letter A is entered. If the user presses the two key twice, the letter B is entered, and if the user presses the two key three times, the letter C is entered. Pauses between entry of successive letters of a word are sometimes necessary, so that the device knows when to advance the cursor to the next letter-entry position. For example, suppose a user wished to search for “MSN”, entering the text for the search using a cell phone or other device with a telephone style keypad. Using the multiple-tap approach, the user might press the 6 key to enter the letter M, pause, press the 7 key four times to enter the letter S, pause again, then press the 6 key twice to enter the letter N. As mentioned, the pauses are frequently necessary for disambiguation. Other keys that are present on numeric keypads, such as the pound (“#”) and asterisk (“*”) keys, among other keys, are typically mapped to remaining symbols in the language, or to switch between numbers, upper-case, and lower-case letters.
While the multiple-tap approach is usable in that users can enter any word using only the numeric keys, it can be disadvantageous for quick and intuitive text entry. Typing an input string such as “MSN” that only requires three key presses on a standard keyboard, one for each letter, could require seven key presses on numeric keys using the multiple-tap approach. As compared to using a standard keyboard, using numeric keys with the multiple-tap approach to achieve text entry means that the user presses many keys even for short messages.
Another approach to text entry using numeric keys is the single-tap-dictionary approach. Under the single-tap approach, the user presses the numeric key associated with the desired letter once, even though the numeric key may be mapped to three or four different letters. When the user enters a number sequence for a word, the device attempts to discern the word that the user intended to enter, based on the number sequence. Each number sequence is mapped to a common word that corresponds to the sequence. For example, the number sequence 43556 can potentially correspond to any five-letter word having a first letter G, H, or I, since the 4 key is usually mapped to these letters. Similarly, the sequence potentially corresponds to any five-letter word having a second letter D, E, or F, a third and fourth letter selected from the letters J, K, and L, and a fifth letter M, N, or O, since the 3, 5, and 6 keys are usually mapped to these respective letters. However, because the most common five-letter word corresponding to the number sequence 43556 is the word “hello” in one example, the single-tap approach may always enter this word when the user presses the 4, 3, 5, 5, and 6 keys in succession to input this number sequence.
The single-tap approach can have advantages over the multiple-tap approach, but can also present new disadvantages. Advantageously, the single-tap approach helps to ensure that the user only has to press the same number of keys as the number of letters in a desired word. For example, the multiple-tap approach requires the user to press the 2 key six times to enter the word “cab”. Conversely, the single-tap approach potentially only requires the user to press the 2 key three times to enter this word, assuming that the number sequence 222 is mapped to the word “cab.” Therefore, the single-tap approach can be more key-efficient than the multiple-tap approach for text entry using numeric keys. It can also be almost as key-efficient as using a standard keyboard that has a single key for each letter.
The single-tap approach can be disadvantageous relative to the multiple-tap approach in that the word mapped to a given number sequence may not be the word the user intended to enter by inputting the sequence. For example, the numeric key sequence 7333 corresponds to both the words “seed” and “reed.” Because only one word is mapped to each numeric key sequence, the word “seed” may be entered when the user keys in the numeric key sequence 7333, whereas the user may have intended to enter the word “reed.” The single-tap approach is especially useful where there is only one unique word for a given numeric key sequence, or, if there are a number of words for a given sequence, when the user wishes to input the most common word associated with the sequence. Where the word mapped by the single-tap approach is not the intended word, text entry may revert back to the multiple-tap approach or to an error-correction mode. Ultimate text entry of the intended word may then require more keystrokes than if the user had started with the multiple-tap approach.